56K V.92 Data, Fax, and Voice Chipset

bytes of fax data before sending it to the remote modem (AT+FTM command). If the modem detects the two terminating characters <DLE><ETX> within the data stream, it transmits the data immediately to the remote modem without waiting for the buffer to fill up.

Table 5-2. <mod> Selection Table

Value

Modulation

Speed

(bps)

 

 

 

 

 

3

V.21 ch 2

300

 

 

 

24

V.27 ter

2400

 

 

 

48

V.27 ter

4800

 

 

 

72

V.29

7200

 

 

 

73

V.17

7200

 

 

 

74

V.17 with short train

7200

 

 

 

96

V.29

9600

 

 

 

97

V.17

9600

 

 

 

98

V.17 with short train

9600

 

 

 

121

V.17

12,000

 

 

 

122

V.17 with short train

12,000

 

 

 

145

V.17

14,400

 

 

 

146

V.17 with short train

14,400

 

 

 

 

 

 

When the modem transfers data to the DTE, the DTE must filter the data stream by removing all character pairs beginning with <DLE>. The DTE also must recognize <DLE><ETX> as the stream terminator. Upon detecting <DLE><DLE>, the DTE must reinsert a single <DLE> in its place. The modem buffers up to 512 bytes of fax data received from the remote modem if the DTE cannot read the data immediately (AT+FRM command).

For the AT+FTH and AT+FRH commands, data is sent and received using HDLC formatting. The format for HDLC framing is provided below. When sending the HDLC data, the modem automatically generates the flags and the frame checking sequence (Frame Check Sum). All the other fields are transmitted to or received from the DTE (that is, these fields are under the control of the DTE).

 

 

 

 

Facsimile

Facsimile

Frame

 

 

 

Address

Control

Checking

 

Flag

Flag

Control

Information

Flag

Field

Field

Sequence

 

 

Field

Field

 

 

 

 

 

(FCS)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 5-1. T.30 HDLC Frame Format

74

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Programmer’s Guide

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Intel MD566X manual Mod Selection Table, Value Modulation Speed Bps